Hot water recirculation plumbing

I have a conventional 50 gallon hot water system with a recirculation pump and separate return line which returns to the bottom of the tank at the drain connection; all pretty standard stuff.

I notice however that when showering, the hot water seems to deplete more quickly when the pump is running. I'm thinking that by circulating the hot water back into the bottom of the tank, then hot and incoming cold water are being mixed and circulated when showering which cools all the water in the tank more quickly.

It seems to me that it would be better to have the return hot water line enter the tank near the upper portion of the tank, in this case at the pressure relief connection point on the side. This way the hot water all stays at the top of the tank and the incoming cold water enters and stays at the bottom of the tank ready to be heated.

You know absolutely nothing about a recirculation system, and your diagnosis is faulty. Connecting it to the T&P valve opening would violate EVERY plumbing and Underwriters's codes. More likely is that the check valve, if you have one is broken.

While you can run the recirc pump continuously, some systems do that, but have a thermostatically controlled valve that shuts it down when the water is already hot. The unit I have, only runs the pump when the point of use is not warm enough, then it runs (typically less than a minute), then shuts off. It may only runs 3-4x per hour. Lots of on/off cycles, which may be lousy for the pump, but it's lasted now for over 7-years without issues. If you ran the return into the top of the WH, it would potentially end up diluting the hot that's there, since it would cool off after flowing both to the point of use, and all the way back to the WH again. Standard operation is to return it to either the cold line, or the drain location if the tank doesn't have a dedicated recirculation port. FOr a long shower, to extend your hot water for showering, consider a drain water heat recovery system. Do a search, and you'll find lots of discussion on them here in this forum. And, check your recirc's check valve is still working as HJ mentioned.

My original configuration had an aquastat to cycle the pump and shutoff valve based on return water temp but I was unable to find a place to put it that adequately monitored the temp up by the faucets. In the winter, the water in the walls cools quickly, while the water in the basement return pipe stays warm so the pump would not cycle frequently enough; I went back to continuous operation with a timer that runs the pump only during peak usage hours. I do have fairly new check valves in each branch and they seem to be working.

With continuous operation, the water in the entire recirculation loop is hot, so my thinking was to return it to the top of the tank. (my plan was to tee into the T&P connection which would bring the T&P valve outward about 3 inches; seems to me it would still function properly)

I think it is a bad idea. The return flow will be cooler than the tank outlet and so will cool the T&P, defeating its intent. Listen to hj, despite his bedside manner. If you think it is a blending problem, my guess is you used too large a recirc pump. Try reducing the flow on the recirc with a dole valve.

When the recirc is off for any length of time, you are probably experiencing a phenomenon known as temperature stacking which results in water that is hotter than the high limit stratifying at the top of the tank. When there is no hot water use for some time, this stacking effect minimizes as the temp evens out throughout the tank. The recirc pump will not let the stacking occur.

If you don't have adequate hot water for the shower, you may consider raising the temp a bit as long it doesn't present a scalding risk.

Another especially hazardous condition is known as the "stacking effect," this is more pronounced in gas water heaters due to the aggressive manner in which they heat water. This stacking occurs due to the natural rise of hot water in the tank, kind of like stacking pancakes, each at a different temperature, cooler ones below and the hot ones stacked on top. As an example, a water heater set to maintain 130ÂºF without a circulation pump could have water temperatures between 130ÂºF at the bottom and 190ÂºF at the top, a very hazardous condition.

My "bedside manner" changes according to the situation, and when someone is obviously not diagnosing the problem correctly and is thinking about creating an "unsafe" condition, it goes into "overdrive" to "hit him with a 2x4" and adjust his thinking. His system is NOT operating normally, but there are many possible causes, just NOT the one he thinks it is, and we would have to be there to see the actual situation and do our own testing to detemine the solution.

I fully agree with you and was not trying to be derogatory. The OP is misdiagnosing the problem and proposing an absurd solution.

When it comes to bedside manners, I would be the proverbial pot calling the kettle black. There is however sometimes a fine line between getting someone's attention with a slap upside the head and losing them altogether. I was just trying to bring him back with the "good cop" routine.

No offense taken and I very much appreciate your good thoughts and comments provided here. I knew you'd come up with some good perspectives and better ideas. I'll noodle these around a bit. As a first step, I'll try reducing or even shutting off the recirc flow during the shower to see how that affects things.

A single central mixing valve would not be compatible with the way you currently have the recirc setup. The recirc loop would have to be on the upstream side of the mixing valve(s).

Where to plumb in one or more mixing valves depends on how your piping branches off. Anywhere there is a risk of scalding would be plumbed after the mixing valve but the recirc loop would have to be before it.

Tapping in before it for the dishwasher though could give you cleaner dishes. Some dishwashers preheat the water based on a timer and the hotter the water going in is, the hotter it will be after it is heated further. Some folk set the water temp higher than is allowed by code so that they get cleaner dishes.

BW has a feature in one of their tempering valve add-ons that provides a tap for untempered water for things like the DW. This may or may not be easy to retrofit, but isn't a bad idea. Hotter water is usually cheaper to produce in the tank than it is having the DW do it via electrical resistance heating, and, it can make the cycle faster.